The thing is we are talking volume, not area. Volume is radius squared times height, thus the master cylinder must travel exponentially to make up for the increased volume not just for one piston cylinder but for four pistons in the larger front calipers. Say the NA is 2 and the SRT is 2.2 in diameter. 2 x 2 =4 but the SRT is 2.2 x 2.2= 4.84. Now .84 x the four pistons would mean the same master cylinder must move 21% more fluid to fill the cylinders. 19.36 vice 16. Everything else being equal the travel of the brake peddle travels 21% farther. That's a bit simplified, but you get the idea. I am no mathematician, so I maybe all wet.
Wish you had more than one other SRT 6 to compare with your car. Plus each car is a little different and even more so with the passing of time.